Vanessa, Michael, Philip
I can explain something about Cattleyas and Lealias. They are epiphytes in the majority, grow at the branches of trees, and the Atlantic Forest trees are tall and close to each other. Some grow over the top branches, some over the middle branches. The adaptation of sending away lots (some times milliions) of seeds, is a response to the difficulty of falling over a branch, as the wind transport them. At the branch, they have to deal with short nutrients, and the existence of mycorryzae fungi is a solution to transform and transport nutrition load.
Other plants have larger and heavier seeds, as the easy target is the soil. At the soil, protection againts predation is offererd by the tegument, and the seed counts with a nutrient reserv, both contributions to heavier weight.
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